Semiconductor devices which use high power generally require a heat sink to dissipate the generated heat. The semiconductor die is mounted on a flag portion of the leadframe, which serves as a heat sink. In order to reduce the size of the moulded package, it is desirable for a lead portion of the leadframe to extend over the die to enable short electrical connections therebetween.
Various leadframe structures are known to provide a lead portion overlapping the flag portion. In one known structure, the lead portions are simply bent out of the plane of the flag portion and then bent back again into a parallel plane over the flag portion. However, this causes the outer dimensions of the leadframe to be decreased by the distance between the two planes. If the outer dimension of the leadframe is reduced, then the automatic handling of the leadframe becomes more difficult because known leadframe handling machines operate on fixed leadframe dimensions.
Another known method of providing the lead portion overlapping the flag portion is to manufacture two separate leadframes, one having the lead portions and one having the flag portions and then connecting, for example by welding, the two leadframes together in the correct position with lead portions overlapping the flag portions. However, such manufacture is clearly more complicated, uses more material and is consequently expensive. Furthermore, it is more difficult to ensure accurate alignment of the flag and lead portions before the welding takes place.